单项选择题

One of the extraordinary qualities of glass is that it can carry ______.

A．light signals
B．sound signals
C．electric signals
D．any signals
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单项选择题
According to the passage the new telephone communication system ______.
A．has been put into actual use
B．was put into actual use in 1977
C．was put on experiment in 1977
D．had been repeatedly experimented on before 1977
单项选择题
According to the passage, people started to make glass ______.
A．4,500 years ago
B．nearly 4,500 years ago
C．less than 4,500 years ago
D．no less than 4,500 years ago
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